In the field of computer hardware and software technology, a virtual machine is a software implementation of a machine (computer) that executes program instructions like a real machine. Virtual machine technology allows for the sharing of, between multiple virtual machines, the physical resources underlying the virtual machines.
In virtual machine environments, a hypervisor running on a host hardware system creates a virtual system on which a guest operating system may execute. The virtual system includes a virtual storage volume on which the guest operating system stores its data. For example, the hypervisor may simulate a hard disk for the guest operating system that the hypervisor stores as a virtual disk file on the host system. Some hypervisors continually track and record changes to the virtual disk file in a changed block list.
A virtual storage volume within a virtual machine contains data items that need to be accessed and scanned. In most cases, accessing the underlying contents of a storage volume can be very resource-intensive, reducing the performance of a virtual machine and other operations within a virtual machine environment.